[/quote]As previously mentioned the imbalance at low volume is usually down to the volume pot not tracking together. One way to get around it if you do a lot of low level listening is to get some RCA attenuators and fit them on the inputs, this then moves your listening range to a higher setting on the pot where it tracks better.
The NAD C315BEE is unusual in that it has an internal adjustment for low volume settings. I am guessing that when your amp is returned from NAD that they will have just tweaked this and balanced the channels better.
I smuggled some attenuators to Mexico and they do the job perfectly, I bought 12db ones and they are a bit to efficient (they attenuate a lot probably 6db for the next time)